This invention relates to a polyolefin resin composition having excellent light-shielding properties, a small specific gravity, a good shock resistance, an excellent stiffness and a good fluidity at the time of molding.
In recent years, polyolefin resin compositions have been investigated as molding materials for electric parts andd automobile parts such as meter boxes, lamp housings and indicator panels for a variety of measuring instruments.
These parts in such fields are required to have betterments such as improved light utilization of a light source, a reduced consumption of electric power, and a less wall thickness and a lightened weight of the parts, therefore it is desired as properties of each molding material that light shielding properties are excellent and a specific gravity is small.
Further, in view of the fact that such parts are practically used after incorporated into various apparatuses or appliances, the molding articles are also required to be excellent in a shock resistance and a stiffness. Futhermore, from the viewpoint of a manufacturing process, it is also important that the molding material has a good fluidity and a sufficient moldability.
Considering the improved light shielding properties mentioned above, the molding material should have a white color rather than a chromatic color such as black color, because the white color is advantageously high in a light reflectance and is also excellent in the light shielding properties.
Thus, there is known a method in which a white pigment is blended with a molding material. In the case that such a white pigment is blended therewith, however, a great amount of the white pigment such as titanium oxide which is high in density and which is expensive is required in order to provide the molding material with the sufficient shielding properties. Therefore, such a method will make the weight of molded articles heavier and at the same time same time the cost of molded articles will become expensive, which facts are contrary to a contemplation of lightening the weight and are not preferable in view of cost.
A method has been suggested in which titanium oxide and talc are together blended with a material (Japanese Unexamined Patent Publication (KOKAI) No. 109235/1981), but sufficiently satisfactory results have not been obtained according to this method.